#include <bits/stdc++.h>
using namespace std;
#define PI 3.1415926
#define   SQUARE(x) ((x)*(x))
//double SQUARE(double x) { return x*x;}

long long f[100]={0,1,1};
int main()
{
	int n;
	for(int i=3; i<=46; i++) f[i] = f[i-1] + f[i-2];
	scanf("%d", &n);
	printf("%lld", f[n] );
  return 0;
}
